The pH values of the extracts give an indication of the acidity or alkalinity of the fiber and its water-soluble impurities. These values are useful in indicating previous processing and in anticipating subsequent performance. For particular purposes, the pH of an extract prepared by one method may be a more informative index than another and as a consequence four optional extraction procedures are included.

This test method is not recommended for acceptance testing because the between-laboratory precision is relatively poor. In some cases, the purchaser and the seller may have to test a commercial shipment of one or more specific materials by the best available method, even though the method has not been recommended for acceptance testing of commercial shipments. In such a case, if there is disagreement arising from differences in values reported by the purchaser and the seller when using this method for acceptance testing, the statistical bias, if any, between the laboratory of the purchaser and the laboratory of the seller should be determined, with each comparison being based on testing specimens randomly drawn from one sample of material of the type being evaluated.